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FreeBSD-SA-23:05.openssh                                    Security Advisory
                                                          The FreeBSD Project

Topic:          ssh-add does not honor per-hop destination constraints

Category:       contrib
Module:         openssh
Announced:      2023-06-21
Credits:        Luci Stanescu
Affects:        FreeBSD 12.4
Corrected:      2023-06-05 16:04:15 UTC (stable/12, 12.4-STABLE)
                2023-06-21 05:43:42 UTC (releng/12.4, 12.4-RELEASE-p3)
CVE Name:       CVE-2023-28531

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

OpenSSH is an implementation of the SSH protocol suite, providing an
encrypted and authenticated transport for a variety of services, including
remote shell access.

II.  Problem Description

When using ssh-add(1) to add smartcard keys to ssh-agent(1) with per-hop
destination constraints, a logic error prevented the constraints from being
sent to the agent resulting in keys being added to the agent without
constraints.

III. Impact

A malicious server could leverage the keys provided by a forwarded agent that
would normally not be allowed due to the logic error.

IV.  Workaround

No workaround is available.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/SA-23:05/openssh.patch
# fetch https://security.FreeBSD.org/patches/SA-23:05/openssh.patch.asc
# gpg --verify openssh.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/12/                                                        r373093
releng/12.4/                                                      r373104
- -------------------------------------------------------------------------

Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=271839>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-28531>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-23:05.openssh.asc>
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